Abstract Detail

Obligate to facultative shift of two epiphytic Lepisorus species during subtropical forest degradation: Insights from functional traits.

Epiphytic ferns are an important group of plants strongly affected by sudden changes in forest community composition and structure. However, a key gap persists in our understanding of their responses to forest degradation, specifically concerning the changes in species distributions and functional traits and their underlying mechanisms. Here, we investigated the vertical distribution of two Lepisorus species of a subtropical primary forest and its two-stage degraded forests in Southwest China, and measured 18 plant functional traits of individuals growing in terrestrial (i.e., on the ground) and 0.5–2.5m epiphytic forest habitats. We found that the relative abundance of both species peaked at heights of approximately 8–16m in the canopy of primary forest but at heights of 0–4m on tree trunks in two degraded forests. Terrestrial individuals occurred only in secondary forests, and the relative abundance of these two species on lower tree trunk and forest ground increased with canopy openness within degraded forests. Principal component analysis of the epiphytes’ functional traits and plasticity provided evidence for two suites of traits related to light acclimation and nutrient strategies. Furthermore, variation in both species’ morphological and physiological traits revealed resource use trade-offs in response to forest degradation. Epiphytic individuals in primary forest had higher capacity for light capture while those in secondary forests had a higher photosynthetic capacity and resource-use efficiency. Within the same secondary forest, terrestrial individuals tended to acclimate to a low-light understory and were more efficient in their nutrient use than epiphytic conspecifics. Together, these results showed a shift of two obligate epiphytic ferns to be facultative in secondary forests, and underwent a downward shift in their microhabitat occupancy to lower tree trunks and understory soils in response to forest degradation. They could achieve this shift by adjusting their functional traits at an intraspecific level, which promoted rhizome extensions to find optimal habitats for persistence.